The experiments in this proposal will investigate patterned connections in two central visual pathways in the cat. In each case, our goal is first to confirm current information on the arrangement of these connections in normally reared cats, using a sensitive labeling technique, an alternative method of sectioning the brain, and quantitative analysis of labeling patterns. Preliminary data indicate these studies will also extend previous findings significantly. Then these same techniques will be used to study cats subjected to various forms of visual deprivation, in an effort to establish the roles of genetic and environmental factors in guiding the formation of these connections. The experiments in the first part of this proposal will examine the overall pattern of thalamo-cortical innervation in the visual cortex of normally reared and visually deprived cats. Connections will be revealed by transneuronal transport of a tracer from the eye to areas 17 and 18, and qualitative and quantitative techniques will be used to describe the labeling patterns in tangential sections taken through unfolded and flattened cortical tissue. The results of these experiments will significantly extend earlier findings, and they will complement contemporary data from behavioral, single-unit recording, and single-cell labeling studies. The experiments in the second part of this proposal will examine the overall pattern of visual interhemispheric connections in normally reared, visually deprived, and retinally lesioned cats. Callosal connections of the posterior neocortex will be revealed by antero- and retrograde transport of tracers, and studied in tangential sections. These studies will characterize the overall visual callosal pattern in the cat, describe its relationship to cortical retinotopy, and reveal the roles of retinally based factors and/or patterned activity in guiding its formation.